of the diseconomies (costs) of population growth that extend beyond the parents and the immediate family and impinge on the welfare of other members of the society. Though these social diseconomies of population growth are undoubtedly substantial for many societies, empirical evidence of their real magnitude has not yet been systematically collected. If our current stock of knowledge and the capacity of our analytical tools are not up to the task of quantitatively estimating the consequences of population growth on the development process, it is, nonetheless, possible to describe qualitatively the effects of rapid population growth as seen at the aggregate and family levels. For analytic purposes, the implications of rapid population growth can be divided into two components: those which are associated with rapid population growth in the very long run, and those which arise in the short run when the rate of population growth changes. In general, a more rapid rate of population growth contributes to a somewhat younger composition of the population, and a broader based age pyramid (46). In the long run, the population of labor-force age grows at the same rate as does the total population, creating a need to add more rapidly to the stock of human and physical capital. To sustain any existing capital-labor ratio, a more rapidly growing labor force requires a higher savings rate.* But the development process is more than a homogeneous process of factor augmentation. Development may be better analyzed as a process that draws an increasing share of the population into distinguishably different and more productive activities. These economic activities require more capital services and other modem inputs per worker than are used elsewhere in the economy; and because they are less routine, they typically require of the labor force more education and skills to cope with their increasingly complex and changing modes of production. The rate at which labor is absorbed into this modern sector of the economy is restrained, and the development process prolonged, by rapid population growth, for many new jobs require that a greater share of output must be saved and invested. In this model of structural change in a dual economy, the savings constraint on development is exacerbated by rapid population growth (33). In the short run, changes in the rate of population growth can impose further burdens on the family and society, depending on the sources of these changes and their effect on the age structure. The reduction in death rates that initiated the postwar increase in population growth rates affected infants and young children more than other age groups. This rapidly growing younger *For example, if we conservatively assume mat the marginal capital-output ratio is equal to the average ratio of, say, three, then a net savings rate from output of 9 percent is required to accommodate a 3 percent annual growth in the labor force without deepening the capital stock or increasing per capita income. This stable state could be achieved with only a 6 percent savings rate if the labor force grew at 2 percent per year.macro-analysis docs not seem to be a rewarding endeavor. (1, Vol. Ill, Appendix 7, pp. 2067-2075.) See also the chapter by Leibcnstein in this volume.